Dual rotation coaxial propeller mechanism



June 1, 1954 E. M. FRANKLAND 2,679,907

DUAL ROTATION COAXIAL PROPELLER MECHANISM Filed May 18, 1950 3 Sheets-Sheet l June 1954 E. M. FRANKLAND DUAL ROTATION COAXIAL PROPELLER MECHANISM 3 Sheets-Sheet 2 Filed May 18, 1950 INVENTOR.

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BYFBI Filed May 18, 1950 June 1954 E. M. FRANKLAND ,9

DUAL ROTATION COAXIAL PROPELLER MECHANISM 3 Sheets-Sheet 3 mi iii "IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII v INVENTOR. l'arlMHanK/and BY Patented June I, 1954 DUAL ROTATION "COAXIA L. PROPELLER MECHANISM Earl Mi-Frankland, Mane to United iAirci-aft hester, 001111., assignor "Corporation; East 'fla'rtform' Conm; a= corporation of Delaware Application *May'18; 1950, Serial No.'162,728

9 EClaims. (01. 1701-13527) This-invention relates to dual rotation propel-- lers and' more specifically to "improvements-Tor interconnecting the several-units of such propellers.

It' is an object of this invention to provide 'an improved inter-propeller "mechanism and hous-' ing for dual-rotation 'propellera Another object of this invention'is to provide an interpropeller housing for dualrotation-propelle'rs which housing is normally stationary relative tothe rotating propelle'r units whereby the-sealing: means-interposed between the propellerunit's and-the housing is subjected to'rela tive rotational speeds --which are equivalent to the-rotational velocity propeller units.

substantially ofone of the Another object of this invention is to provide a -drive' for the integral pumps of dual rotation propellers whereby the normally stationary interpropeller :housing is operatively connected to the pumps-so that L during propeller 1 rotation the pumps. will be dri'ven 'at .a rotational speed equivalent to the speed of any one-propellercomponent. Afurther objectof this-invention is to provide means for transmitting power from one rotating unit: to .another'of a dual rotation propeller whereby the-z cooperating electrical connectors arei'subjiectedtorelative speeds not in'exces's of that of any :one propeller component A'.Stl1l' further object of this invention is to provide a synchronizing-mechanism for the blade settings tofithe several rotating units 1 of a dual rotat-ion :propeller. which comprises gear trains interconnecting the units and spanning-the axial space therebetween;

Another'objiectt of this invention is to-provide a stationary housing 'for a synchronizing mechanism of: the .type described whereinthe housing carries -'some of .the gear elements and provides a- -fluid. tight chamber surroundingthe gear mechanism; this fluid chamber thus: forming an axial extensioniof;andlcommunicating with, a lubricating ichamber. carried by the outboard "or forward propeller unit.

These and other objects of this invention will become readily-apparentfrom the following detail description'of the accompanying drawings in which:

Fig. l is an illustration of .a dual rotation propeller having an interp'ropeller housingconstruc tion according to this invention...

Figr2is a cross-sectionalview of Fig. 1 with portions. of the section taken along arbitrary planes. to' conveniently illustrate the majority of the operating units.

Fig. 3 is a schematic showing of the Fig. 2 illustration.

Fig. 4-is a perspective and schematic showing of theinter propeller connecting mechanism;

Fig; 5is a detail cross-sectional View of the intershaft sealing mechanism.

Referring to Fig. l, a dual rotation propeller is shown having an inboard unit and an outboard unit 22, respectively, each of which include the hubs 24 and 26, respectively, and'a pluralityof blades 28 and30mounted for pitch changing movements relative to the hubs. Thepropeller units are driven by a power plant in opposite directions at'a fixed ratio or equal speeds by a well-known'mea'ns omitted herein for convenience. The propeller units 20 and 22 include an interconnecting mechanism therebetween including a housing which normally remains stationary during propeller rotation whereby thesealingmechanism 46 interposed between the'outb'oardpropeller unit 22 and the housing 44 'and the sealing mechanism 48 interposed between the inboard propeller unit 20 and the housing 44 are subjected to only one-half the relative velocity betweenthe two propeller units. In other words, the sealing *mechanisms 45 and 48 are subjectedto a relative rotational velocity which is "substantially equivalent to that of only one of the propeller units. 7

The pitch of the propeller blades '28 and 30 may be'varie'd by'means of fluid operated motors such 'as for example illustrated and described in patentapplication-Serial "No. 154,857, filed April 8;"1950j'by Arthur N. Allen, Jr. and now Patent N 052,667,229;

In" order'to" properly synchronize and coordinatethe pitch changing movements ofthe blades of-" the several propeller units, it is desirable'to'provi'de' a-simple yet elficient interconnecting mechanism between these propeller. units.

hub-24:15- driven by an outer Shaft While the outboard'propell'er hubZS is driven by an inner 280i the inboard hub-24 Thusythe blade syn chronizinggear at of "the inboard'hub 24 includes a forward extending sleeve 64 which has a To this end "(Fig 2) the inboard prop splined connection with a ring gear 68 which in turn meshes with a gear 68 journalled within the hub 24. The gear 68 drives another gear by means of a common shaft 12. The gear 10 meshes with a ring gear 14 which is carried by an aft extending portion of a freely rotatable sleeve 16 forming a part of the interpropeller connecting mechanism contained within the aforementioned housing 44. The sleeve 16 has a forward extending portion 18 which carries a ring gear 80. The ring gear 80 is connected to another ring gear 82 of similar diameter by means of a plurality of reversing gears, described hereinafter in connection with Figs. 3 and 4, so that when the gear 80 is driven in one direction, the gear 82 will move in an opposite direction. The gear 82 is carried by a freely rotatable sleeve 84 which in turn carries a cam track 86 located within the aft portion of the outboard hub 26. A cam follower 88 cooperates with the cam track 80 in such a manner that rotation of the sleeve 84 will cause the cam follower S0 to rock about its pivot 00 so as to reciprocably move the spool 92 of the distributor valve 80. The distributor valve 60 in turn will direct high pressure fluid to the propeller pitch changing motors of the outboard hub unit 26 and change the pitch of said blades as described in detail in the above-referenced patent application.

The high pressure fluid may be provided by a pump I00 which takes in fluid from a pressurized sump I02 and directs it to the distributor valve 60. The pump I00 is carried by the hub and is normally driven in response to propeller rotation by a gear I04 which is interconnected to a gear I06 fixed to the normally stationary interpropeller housing 44. Thus the housing 44 serves as a pump drive during propeller rotation in addition to having utility for other purposes described herein. By connecting the pump gear I04 to the housing 44 the pump I00 can be driven at a speed substantially equal to the rotational speed of one of the propeller components.

During the pitch changing movements of the blades of the outboard hub 26, the blade synchronizing gear IIO which interconnects each of these blades will be rotated an equivalent amount. The blade interconnecting gear IIO has a splined connection II2 to a blade follow-up gear I I 4 which in turn is capable of rotating the gears I I6 and I I8 carried by a common shaft I20. An adjusting mechanism 124 is provided for adjusting the position of the shaft I20 and the gears carried thereby relative to the blade follow-up gear H4. The blade follow-up mechanism and interconnecting gearing just described is connected by means of a second gear train to the hub 24 of the inboard propeller unit 20 in a manner now to be described. To this end, the gear I I8 on the shaft I20 engages a gear I30 freely rotatable on a spindle I32 journalled within the hub 26. The gear I30 also engages a gear portion I34 carried at one end of a freely rotatable sleeve I36 which carries at its other end a gear I38. The gear I38 is interconnected in turn to a gear I40 of similar diameter by means of a reversing gear mechanism also to be described hereinafter. The gear I40 is carried by a freely rotatable sleeve I42 which is splined at I44 to a sleeve I45 fixed to the inboard hub 24 by means of bolts I48.

The reversing gears mentioned hereinbefore are journalled within the interpropeller housing 44 in such a manner that during the equal and opposite rotation of the propeller hubs 26 and 24 the entire housing 44 normally remains stationary. The housing 44 includes a substantially annular outer wall portion I and an integral sleeve I52 which is radially spaced inwardly from the wall portion I50. The sleeve I52 is fixed to an outer ball bearing race I54 which in cooperation with the balls I56 and an inner race I58 serves to support the entire housing 44 on the retating inner concentric drive shaft 52.

The forward extremity of the wall I50 carries a rubber U-shaped seal I60 held in position by a garter type spring I62. The upstanding portions of the seal I60 cooperate respectively with a pair of depending flanges I04 and I66 which are fixed by means of bolts I68 to a rear closure member I10 of the hub 26.

The closure member I10 forms a chamber I12 which is normally at atmospheric pressure and accumulates lubricating oil which is supplied to the gears located therein. Although not illustrated herein, a scavenging pump normally takes fluid from the chamber I12 and exhausts it at a certain pressure into the pressurized sump I02 from whence it is taken by the high pressure pump I08 and fed to the distributor valve 60. The pumping system just described is shown in more detail in the above-mentioned co-pending patent application. The aft axial extremity of the Wall I50 carries a depending flange I which cooperates with a rubber seal I82 fixed by a garter type spring I84 to a sleeve I86 which in turn is fixed to, and rotatable with, the inboard hub 24. It is thus apparent that since the housing 44 is normally stationary relative to each of the propeller units, the seals I60 and I82 adjacent the fore and aft extremities respectively of the housing 44 will be subjected normally to no more than the rotational velocity of one of the propeller units. It is further apparent then that the housing 44 spans the axial space between each of the propeller hubs 24 and 26 so as to form a fluid tight closure member for the gear mechanism which interconnects the operating units in each of the two propeller components.

As further viewed in Fig. 2, it can be seen that the outer concentric drive shaft 50 terminates at I90 adjacent the inboard propeller hub and has a retaining nut I92 threaded thereto for fixing the hub 24 thereto. Therefore, it becomes necessary to provide a sealing mechanism, generally indicated at I96, between the drive shafts 50 and 52 so that lubricating fluid within the interpropeller housing 44 will not drain back toward the engine or power plant 40. The sealing mechanism I96 is more clearly illustrated in Fig. 5. As viewed herein, the concentric shaft 52 extends forward of the end I90 of the outer drive shaft 50 and the sealing mechanism I96 is interposed between the forward (outboard) extending portion I08 of the inner shaft 52 and the inner periphery of the retaining nut I92. The sealing mechanism I90 comprises a collar 200 which is fixed for rotation with the inner shaft 52, a carbon seal ring 202 and'a shoe 204 which is rotatable with the outer shaft 50 and engages the inner periphery of the retaining nut I02. The shoe 204 is biased against the carbon ring 202 by means of a spring 205 which is partly enclosed in a hollow plug 208 which engages a tapered wall portion 210 of the retaining nut I92. It is then apparent that the sealing mechanism I06 just described and the seals I00 and I82 adjacent the extremities of the interpropeller housing 44 serve to completely enclose the interprepeller gear mechanism and form a fluid tight chamber which is in communication with the on -the.-;inner-drive shaft 52;

pastetheseroller bearings 242 will, of course; be

lnim heaftend;ofthe 'olllibQalid hllb i'eferr n asa nrto-aE g. 2;:1ubricating-means providd;rfo11-the;gearsqhoused within the housing Mbmmeansgofl aqsleeve 2-301which includes a plu ralitytof axial; slots 232 spaced apart on itsinner periphery, The-slots. 232. communicate with: an annular groove 234 which,receives-lubricating fluid.;.;under"pressurea from a source-within thehl1b j26 via; passages omitted for -.convenience Each-of thegroovesitz communicateswith at least one;port; as for-example-zat 236,1to provide. lubricating fluid to the bearings and rotating gears adjacent thereto. It will-be noted that the sleeve;-23 0 extends aft-of: the hub-Zliso that the rea r .inb oarde tending portion 240" thereof is: rad lly;;spa;ced,.from-the inner shaft: 52 films:

for ng an annular chamber 24l Eachofthe sl9ts 232;in the sleeve-fit extendginto theichamber- 52. I 150" that lubricating fluid can flow in an: inboardflirection, asindicated by the-arrowsin:

Qrder"tm-lubricatethe mainroller bearings 242 which; supportthe forward portionof the hub 2 4- preyented from flowing inboard between the driveshafts 50, and 52 by the sealingmechanism I 96.;previously described,

Inasmuchas-the. interpropeller housin 4-; is normally stationary-relativeto the propeller units and the gears therein are :normally rotating, any exeessioilzwhich thrown outwardly by the gears or otherwise accumulates invthecasing will tend toidraingintaa forwardi direction into the chamber lgl2zin, the attend-pf. the outboard'propeller unit.

n: orderto-rprovidea transferof electrical poWenfrom the inboardhub 24 {to the outboard hub 26 the housing 4 3 is also utilized to carry-a brushzassembly .2511 :which. includes. a plurality of conducting gbrushes'.25I,- 252 vbiasedwapart bya spring-.-25.3. The brushes 25! engageannular slip rings 254 on the outboardside of theinboard hub 2.4;while the brushes 2.52 engage .annularslip rings 255- on theinboard .endpof'the. outboard hub 26.. Theisprings;253-:mayserve to conduct-current between; brushes 25I and 252.1 Theslipnrings 255- may--in:.turn be operatively; connected to electrically v. operated elements of the outboard .propeller; component particularly electrical. deicingr equipment for theblades -3Bsthereof (omitted for if convenience). It :will benoted that-the relative. speedsibetween the-brushes 25I and the slip rings. 254, ior\betweenthe brushes 252. and255 will be no I more'than the .speedof any one of the respective hubs. To this vend wearand malfunction were reduced considerably.

The gear trains whichprovide the interconnec-t tion between thepropeller units and whic'hare substantially housed'within the interpropeller hOllslIlgAk are =moreclearly illustrated in Figs. 3

and :4. As showntherein; the blades. 28aare connected: by-means of the blade interconnecting gear-55 and thegears Bag-mend "I4 to the gear (ill The gear so :meshes :with the-gear 28! mounted on a shaft 282 which in turnis freely rotatable in bearings 284 carried by the :wall I5oof the interpropeller housing 44.: The gear 280 in turn meshes with another gear 2B6-which is fixed to .a

shaft 283' mountedinbearings-ZQB. Theshaft 288 also has fixedthereto a gear 292which engages-the gear 82. The gear 82 as previously described-is fiXed to,-and integral with, acam track 88 which guides the cam follower-88 soas to pivot the latter. aboutgits ..pivot9llizand thereby actuate IV v the gclistributori valve. Gllzduring pitch :changing; .a

Any fluid moving movement; of ,;thewb:1adesa-on theeinboarde come ponent; When .no-=,1pitchs;changeris;takingiplace however,--sthe:-blade iinterconnecting ear :56 issroa tatingrat;:t-he;v same speed: as the .inboardzshub 24 while the distributor valve and its camifollowing, mechanism .is rotating-iin the opposite i direction: along with the'hub -25: of .the outboard component; Hence, -by;means ofthegear train 8,0., 280,t:286, 2:92; andfiIlZ the icamtracksllfi rotates at the same, speed: asthe cam fol1ower-=88 and the ;valve Bllso thatno pitch changing; movements, are efl'ected'. inzgithe: outboard component; However,; in the event that the blades 25' on the inboard'component are actua atedfor pitch achanging movement in either. di-.; rection; the resultww-ill be that I the :blade interconnecting; earfiE-carried by the inboard hub, 24

will momentarilymove faster :or .slower than the speed of the hub-2on0 that via the gear trainijustt mentioned the camtracie-SS will'slowuponspeed-i their pitch so that the blade inter-connecting gear H8 on the; outboard component ;will rotate relas. tive to; its respective --hub and cause a fasterror; slower movement relative to the outboard :hub .;2Bi through the follow-up gear I I6; gears-8,111 30, I32 and-the gearv I38. As previously mentioned, the gear I38 is connected through-the. elementsloff its reversing ,train'to'the gear-I40 which'is fixed:

for equal and opposite rotation .to the: inboard.-v

hub 24. With this, fixedrelationzth'en the reversing gear elements of the. follow-untrainwhich are journa1led;with: the housing fl will cause the housingtorotate-slightly and to efiect:

the motion 'of' the reversing. gears 280, 286, 292 which are also housedthereinsso that: earn track 85 twillzreturnto a'position whereby the cam follower 88 and the distributor valve fill are no longer calling for a pitch change.

The. above-mentioned reversing gear elements ofzthe follow-up .gear :train which are connected to the gears "l3t andi ldficomprise a gearllll:

meshing with'the gear i313 and carried by a shaft 362 journalle'din bearings304 and-3i5 carried by:-

the walls I5!) of the housing M; The gear -3llfl' meshes witha gear 3H] which is fixedto-ash'ait"v 3J2journalled inzbearingsfi i i and 3 l 6 also carried by the Wall I50. The-shaft 3I-2 '=also has fixedthereto agear 320 Which meshes-with a rin gear- MU carried bythe sleeve 1 42 and is splined-at I44 1 to thehub 240i the inboard propeller component.

Summarizing, then, the general operation of 1 the interpropeller connected gearmechanism (referrin to Figs; 3 and 4) it will be apparent" that since-the'outboard hub 26 'and 'the-inboard hub Mare driven at equal and opposite 'speeds,v

the blade interconnecting gear I I0 carried-bytheoutboard hub-and associated follow-up-mec-h anism H6; He and I30 will be stationary 'rela-- tive to the outboard' hub 26 and-will'rotate' the w gear I34 at the speed ofthe outboard'hub, The

gear IL L in-turn, will causethegear I38 to rotate at an equal and opposite speed relative to the gear-- Mil which is fixeclito, and rotates with, the inboardhub 24;; Hence, the reversing gears 300; 3"]

and 320 which are .journalled in theshousingrdd will maintain the;:ho.using. normally .flxedexcept? Y when'ia :pitch change. is; taking :placeain' the touts board propeller; component With; the housings 7 44 held stationary, should a pitch change take place in the inboard component, a relative increase or decrease in speed is transmitted from the blade interconnecting gear 56 of the inboard hub 24 through the gears 68, i0, i4, 80 and through the reversing gears 28!], 286, 292 and finally to the gear 82 and the cam track 86. Thus, the distributor valve 60 on the outboard component will be actuated in response to pitch changin movement of the blades of the inboard component while the housing 44 remains stationary. Then as previously described, as soon as a pitch change is produced in the outboard component the follow-up mechanism carried by said component will cause the gear [38 via the train H6, H8, 130, 134 to speed up or slow down relative to the outboard component rotational velocity so that the normally equal and opposite relative rotational speed between the gears I38 and M8 is momentarily disrupted so that the reversing gears etc, 310 and 320 will translate this unequal velocity to the housing 44 by means of their shafts 392and 312. The housing 44 will then rotate a slight amount in either direction to vary the relationship between the gears 80 and 82 and their reversin gears 280, 286 and 292 in the pitch change gear train. This variation of relationship will then tend to return the cam track 86, follower 88 and the distributor valve Bi! to a valve neutral position so as to stop the pitch changing movements of the outboard component at a desirable setting.

It is therefore apparent that as a result of this invention a positive and compact synchronizing mechanism has been provided for maintaining the proper pitch change relationship between the blades of the several components of a dual rotation propeller.

F'Lu'ther, as a result of this invention means have been provided for enclosing this synchronizing mechanism in an efilcient manner whereby a fluid tight lubricant chamber is provided. The provision of an enclosure of the type described, which enclosure normally remains stationary relative to the oppositely rotating propeller components, greatly decreases leakage problems due to the fact that the seals between the stationary housing and the hubs of the rotating components are subjected to rotational speeds not exceeding that of any one component. With reduced wear,

leakage is reduced. The same holds true in regard to the relative velocities of the brushes and slip rings which transmit power between the hubs. The importance of this relative speed reduction and wear reduction can be seen by the fact that it is generally known that wear increases somewhere in the order of the cube of the speed. Hence where the speed between relative parts does not exceed that of any one unit the wear is approximately one-eighth that existing where the relative speed is the sum of the units.

Although only one embodiment of this invention has been illustrated and described herein, it will be apparent that various changes and modifications will be made in the construction and arrangement of the various parts without departing from the scope of this novel concept.

What it is desired to obtain by Letters Pat-- changing movements relative thereto, means for changing the pitch of said blades carried by each relative to said hubs, means providing lubricationfluid for said gear means, and sealing means interposed between said shroud and hubs provid ing a substantially fluid tight container which forms an axial extension of and communicateswith said chamber.

2. In a dual rotation aircraft propeller havingfore and aft axially spaced units driven in opposite directions, blades carried by each of said units and mounted for pitch changing movements relative thereto, power actuated pitch changing means carried by one of said units responsive to the blade pitch changing movements of the other of said units including a gear train forming a continuous connection therebetween, a cage surrounding said train and spanning the space be-' tween said units and having elements of said gear train journalled therein whereby said cage nor mally remains stationary during propeller rotation, a power generator carried by said one unit and operative in response to rotation of said one unit for actuating said pitch changing means including a connection to said cage, and conductor means for transmitting electrical power between said units comprising contact elements car'- ried by said cage and cooperating contact elements carried by said units whereby the relative rotational velocity between said elements is normally equal to the rotational velocity of one of said units.

3. In a dual rotation propeller according to.

claim 2 wherein said cage has fore and aft ends and seals are provided between said cage and units adjacent said ends.

4. In a dual rotation aircraft propeller having fore and aft axially spaced units driven in opposite directions, blades carried by each of said units and mounted for pitch changing movements relative thereto, pitch changing means carried by one of said units responsive to the blade pitchfixed to said cage and operatively connected'tm said pump means whereby said pump means is energized at the speed of said one unit with respect to said gear means.

5. In a dual rotation propeller having fore and aft axially spaced hubs adapted to be driven in opposite directions, blades carried by each of said hubs and mounted for relative thereto, pitch changing means carried by one of said hubs operative in response to movement of the blades of said other hub including a first geared interconnection therebetween; and

means operatively interconnecting the blades of; said one hub with said other hub including a secpitch changing movements nd geared interconnection therebetween, each of said geared interconnections including planetary pinions respectively, a cage surrounding said trains, said cage including a journal for each of said planetary pinions respectively, and reversing gears journalled in said cage and engaging said planetary pinions.

6. In a dual rotation propeller having fore and aft axially spaced hubs adapted to be driven in opposite directions, blades carried by each of said hubs and mounted for pitch changing movements relative thereto, pitch changing means carried by one of said hubs operative in response to movement of the blades of said other hub ineluding a first geared interconnection between said pitch changing means and the blades of said other hub, and means operatively interconnecting the blades of said one hub with said other hub including a second geared interconnection therebetween, a cage having pinion gears journalled therein and means operatively connecting said pinion gears to said geared interconnections for positioning said cage in space at a predetermined rotatable position with respect to the pitch position of the blades of said one hub.

7. In a dual rotation propeller having fore and aft axially spaced hubs adapted to be driven in opposite directions, blades carried by each of said hubs and mounted for pitch changing movements relative thereto, pitch changing means carried by one of said hubs operative in response to movement of the blades of said other hub including a first geared interconnection between said pitch changing means and the blades of said 1 other hub, and means operatively interconnecting the blades of said one hub with said other hub including a second geared interconnection therebetween, a planetary cage, a first pair of pinion gears fixed relative to each other and journalled in said cage, said pair of gears forming a part of said first geared interconnection, and a second pair of pinion gears fixed relative to each other and journalled in said cage, said second pair of gears forming a part of said second geared interconnection.

8. In a dual rotation propeller having fore and aft axially spaced hubs adapted to be driven in opposite directions, blades carried by each of said hubs and mounted for pitch changing movements relative thereto, pitch changing means carried by one of said hubs operative in response to movement of the blades of said other hub including a first geared interconnection between said pitch changing means and the blades of said hub, and means operatively interconnecting the blades of said one hub with said other hub including a second geared interconnection therebetween, a planetary cage, a first shaft journalled in said cage, two pinion gears fixed to said first shaft and forming a part of said first geared interconnection, a second shaft journalled in said cage, and two pinion gears fixed to said second shaft and forming a part of said second geared interconnection.

9. In a dual rotation aircraft propeller having fore and aft axially spaced units driven in opposite directions, blades carried by each of said units and mounted for pitch changing movements relative thereto, pitch changing means carried by one of said units responsive to the blade pitch changing movements of the other of said units including a planetary gear train forming a continuous connection between said pitch changing means and the blades of said other unit, said planetary gear train including a cage, planetary pinions journalled in said cage, and driving and driven gears operatively connected for rotation with said units whereby said cage normally remains stationary during rotation of said units, said cage surrounding said train and spanning the space between said units, a planetary gear train connection between said other unit and the blades of said one unit comprising planetary pinions journalled in said cage for moving said cage in response to the pitch changing movements of said one unit whereby said cage is moved to inactivate said pitch changing means, and sealing means between said cage and said units whereby the relative rotation between said sealing means and said units is normally equal to the rotational velocity of one of said units.

References Cited in the file Of this patent UNITED STATES PATENTS France Aug. 16, 1943 

